Electrical switch

ABSTRACT

A snap action electrical switch includes a switch blade mounted on a common terminal for movement between normally closed and normally open terminals. The switch blade includes a tension member which is provided with a depressed portion extending below the ends of the switch blade. A compression member on the blade biases the switch blade into contact with the normally closed terminal and tensions the depressed portion of the tension member. An operating button is slidably mounted above the depressed portion for engagement therewith, and movement of the depressed portion under the influence of the actuating button moves the switch blade into engagement with the normally open terminal. The stresses created in the depressed portion by the actuating button reduce the net stresses in this portion during actuation and thereby prolong the life of the switch blade.

United States Patent 1 1 1111 3,878,347

Roeser Apr. 15, 1975 ELECTRICAL SWITCH Primary Examiner-David Smith, Jr.

[75] Inventor: John O. Roeser, Arlington Heights,

57 ABSTRACT [73 1 Assignee: Otto 'l f A snap action electrical swit eh includes a switch blade Carpentersv1lle,lll. mounted on a Common terminal for movement be- 22 Filed; 4, 1972 tween normally closed and normally open terminals. The switch blade includes a tension member which is [21] Appl- BIO-14397300 provided with a depressed portion extending below the ends of the switch blade. A compression member 52 US. Cl 200/67 D on the blade biases the Switeh blade into Contact with 511 Int. Cl. ..n0111 13/36 the normally closed terminal and tensions the [58] Field of Search 200/67 D, 67 DA, 67 R, Pressed portion of the tension member- An Operating 200 3 p; 337 313; 74 100 p button is slidably mounted above the depressed portion for engagement therewith, and movement of the 56 References Cited depressed portion under the influence of the actuating UNITED STATES PATENTS button moves the switch blade into engagement with 1 the normally open terminal. The stresses created in 2,460,087 1/1949 1101115 200/67 D 3,033,953 5/1962 Schwerke 200/67 1) the depressed actuatlng reduce the net stresses in this portion durmg actuatlon and FOREIGN PATENTS OR APPLICATIONS thereby prolong the life of theswitch blade.

1,590,339 5/1970 Germany 337/318 23 Claims, 14 Drawing Figures 56 58 39 s2 49 42 as H 1 23 1 A/////l 64 ll 31 l 1 as ll III II ll ll I'T/ l 24 l |9 i'| 111 l l ELECTRICAL SWITCH BAckoRouNp This invention relates to electrical switches. and the invention finds particular utility in s'nap action switches which include a switch blade mechanism having a tension member and a compresi'on member.

Many different types of snap action switches are available. Such switches generally include a switch blade which is engageable by an operating buttom to move the switch blade from one terminal to another. A portion of the switch blade acts as a tension member to provide over-center snap action, and a compression member snaps the switch blade back to its original position when the operating force is released.

Some competitive switches use a switch blade comprised of two or three parts. The problems with using a blade formed of a plurality of parts include tolerance buildup of the individual parts, the cost of assembling the parts, and the cost of the several individual parts. Further, some of these switch blades include a small C- shaped compression spring, and this spring is difficult to make accurately and to install. At least one manufacturer utilizes a unitary switch blade, but this switch blade has relatively short lift and tolerance problems.

Many switch blades fail due to flexure fatigue just below the area which is engaged by the operating button. This is a common failure point because maximum bending stress of tension is provided in the blade immediately under the point of load application, i.e., the point engaged by the operating button. Fatigue failures are tension failures. A fatigue failure starts as a crack at a surface under tension. and continual cycling of the loading force on the switch blade can eventually cause blade failure as the crack progresses. Further, the tensile forces created in the switch blade by the compressive spring member provide an initial tension force so that tensile stresses created by the operation button increase the stress within the switch blade which tends to cause fatigue failure.

Another cause of uncertain mechanical life in small switches is the build up of part tolerances that result in excessive compression of the spring member and resultant high leg tension. For example. optimum compression of the spring member might be about 0.010 inch, but tolerance build up of. the switch blade, the C- shaped compression spring, and the supporting yoke might be as much as 0.020 inch. This can cause erratic forces, inoperative switches, or the necessity of individual adjustment.

The problems of prior art switches are particularly troublesome when the switch blade is intended to operate on a very short travel, e.g., of the order of about 0.001 inch. Military Specification Sheet MIL- S-8805/4F specifies a movement differential maximum of either 0.0015 inch or 0.005 inch, depending upon the particular switch, a pre-travelmaximum of 0.020 inch, and over-travel minimum of 0.004 inch, and a differential force of 1 to 2 ounces. The differential maximums and the differential force specifications are difficult for many switch manufacturers to meet. and, while switches are available which meet the minimum over-travel specification, much more over-travel is highly desirable.

Of the switches that do meet the foregoing military specification, most are characterized by one or more of the following problems:

SUMMARY OF THE INVENTION The invention provides an electrical switch with a minimum of parts, including a unitary switch blade. The switch blade includes a tension member having a depressed intermediate portion and a compression member which biases the switch blade into a first position and prestresses the depressed portion of the tension member. The operating buttom engages the depressed portion to move the switch blade to a second position, and the preloaded stresses within the depressed portion subtract fromthe stresses created by the operating button so that the net tension within the switch blade remains relatively low and the likelihood of fatigue failure is reduced. In the preferred embodiment the switch blade includes a pair of spaced-apart legs and a central tongue. Each of the legs has an S- shaped central portion which makes the switch blade very flexible and which readily accommodates any tolerance build-up of the other parts when the switch blade is installed. The central tongue portion of the blade acts as the compression member and prestresses the downwardly extending or depressed portions of the S-shaped legs.

The longer path around the double bends of the legs provides more material in the length of the blade so that flexure is distributed to a greater extent, and the S-shape of the legs serve to keep the line of tension of the blade in the plane and provide desirable clearance around the other elements with the switch. The greater flexibility of the blade also permits relatively large overtravel. The switch can also be made quite sensitive when that is desired, and movement differentials as low as 00005 inch are attainable. The switch has only five components within the switch casing, and only two of these components, the switch blade and the actuating button, are movable. The other three components are stationary terminals. Accordingly, tolerance build-ups. assembly costs, and part costs are minimized.

DESCRIPTION THE DRAWING The invention will be explained in conjunction with an illustrative embodiment shown in the accompanying drawing, in which:

FIG. 1 is a sectional view through a switch formed in accordance with the invention;

FIG. 2 is a fragmentary sectional view similar to FIG. 1 but taken through the switch blade and showing the switch in the actuated position;

FIG. 3 is an enlarged perspective view of the switch blade;

FIG. 4 is a side elevational view of the switch blade without the contact;

FIG. 5 is an end elevational view of the switch blade taken along the line 55 of FIG. 4;

FIG. 6 is a top plan view of the switch blade of FIG.

FIG. 7 is a top plan view of the common terminal;

FIG. 8 is an end elevational view of the common terminal taken along the line 88 of FIG. 7;

FIG. 9 is an end elevational view of the-operating button;

FIG. 10 is a top plan view of the operating button;

FIG. 11 is a fragmentary side elevational view of the switch blade showing the prestressed loading forces on the switch blade caused by the compression spring tongue of the switch blade;

FIG. 11A is an enlarged fragmentary sectional view of the depressed portion of the switch blade showing the forces of FIG. 11;

. FIG. 12 is a view similar to FIG. 11 showing the stresses within the switch blade casued by the operating button as it depresses the switch blade: and

FIG. 12A is a view similar to FIG. 12 showing the forces of FIG. 12.

DECSRIPTION OF SPECIFIC EMBODIMENT Referring first to FIG. 1, the numeral 15 designates generally an electrical switch having a casing 16 from which three connecting terminals l7, l8, and 19 extend. The particular switch illustrated is formed in accordance with Military Specification Sheet MIL- S-8805/4F, but the invention can be used in many different types and sizes of switches. The switch casing includes a base 20 having a pair of openings 21 and 22, and a cover 23 secured to the base. Each of the connecting terminals 17-19 extend through the base into the enclosure between the cover and the base, and each terminal includes a knurled radially enlarged portion 24 which is frictionally engaged with an opening in the base.

A generally U-shaped yolk or common terminal member 26 is secured to the connecting terminal 17 and includes a base portion 27 and a pair of upwardly extending leg portions 28 and 29 which are provided with V-shaped notch as 30 and 31, respectively. A somewhat Z-shaped normally open terminal 33 is connected to the connecting terminal 18 and includes a straight attaching portion 34 and a straight contact portion 35. A generally U-shaped normally closed terminal 36 is secured to the connecting terminal 19 and includes a straight connecting portion 37, an upwardly extending intermediate portion 38, and a straight contact portion 39 which extends above the contact portion of the normally open terminal. Each of the terminals 26, 33, and 36 are formed of suitable electrically conductive material such as silver-coated brass, and each of the terminals are secured against the top surface of the base 20 by peening the upper end of the associated connecting terminal as at 40.

An elongated electrically conductive switch blade 42 formed of flexible and resilient spring metal is movably supported within the switch enclosure by the common terminal 26. Referring to FIG. 3, the switch blade includes a pair of flat end portions 43 and 44, a pair of spaced-apart leg portions 45 and 46, and a tongue portion or center leg 47 which extends from the end portion 44 between the two legs. The end portions of each of the legs are flat and form an extension of the flat end portions 42 and 43, and the intermediate portion of each leg has a general S-shape provided by a depressed portion 48 which curves downwardly from the plane of the end portion 43 and a raised portion '49 which curves upwardly from the plane of the end portion 44. The raised portion 49 has a generally s mooth or arcuate curve, but the depressed portion 48 includes a substantially flat central portion50 which extends substantially parallel to the end portions 43 and 44.

The switch blade is provided with apair of circular stress-relieving openings 52 where the lateral edges of the tongue 47 join theend portion 44 and the legs 45 and 46, and each of the lateral edges of the tongue extends generally tangentially from the associated opening. These openings prevent stress concentration in the areas where the tongue and the legs would otherwise meet. In the particular embodiment illustrated, the openings 52 have a diameter of 0.025 inch, which is considerably larger than any corresponding openings in competitive switch structures known to me. For example, competitive switches of this size commonly have an opening of only 0.005 inch. However, despite the relatively large openings 52, the end portion 44 is provided with sufficient strength by a pair of side flanges 53 which extend downwardly from the lateral edges of the end portion 44. These flanges also serve to strengthen the end portion around the generally rectangular opening 54 (FIG. 6) in which an electrically conductive contact 55 is secured. The side flanges 53 serve the further purpose of providing more material for conducting heat away from the contact.

The switch blade is operated by an actuating button 56 which is slidably received in a cylindrical collar 57 formed in the cover of the switch casing. Referring to FIGS. 1, 9, and 10, the actuating button includes a generally cylindrical finger portion 58 having a rounded top 59 and an elongated actuating portion 60 which extends outwardly from the cylindrical finger portion to provide shoulders 61 and 62. The cylindrical finger portion 58 is slidable within a correspondingly shaped cylindrical portion of the collar 57 of the cover, but upward movement of the button beyond the position illustrated in FIG. 1 is prevented by engagement of the shoulders 61 and 62 with the top wall of the cover. The lower portion of the cylindrical collar 57 is slotted to accommodate the laterally outwardly extending actuating portion 60 of the button, and the engagement of walls of the slot with the actuating portion prevents rotation of the operating button relative to the other parts of the switch.

The collar 57 positions the actuating button above the depressed portions 48 of the legs of the switch blade, and the actuating portion includes a pair of spaced-apart V-shaped switch engaging portions 63 and 64 which engage the depressed portions of the legs 45 and 46, respectively. A centering portion 65 extends downwardly between the switch-engaging portions 63 and 64 and extends into the slot between the spacedapart legs of the switch blade to maintain the actuating button centered with respect to the blade.

The switch is assembled by inserting the connecting terminals 17-19 into the base of the switch casing, inserting the terminals 26, 33, and 36 over the upper ends of the associated connecting terminals. and peening the upper ends of the connecting terminals to secure the terminals. In order to facilitate connection of the common terminal 26 to the connecting terminal 17, the upwardly extending leg 28 thereof can extend parallel to the axis of the connecting terminal 17 until the upper end thereof is peened. as shown in FIG. 7. Thereafter, the leg 28 can be bent toward the other leg 29 to the position shown in FIGS. I and 2.

a The switch bladei's then mounted on the common terminal by inserting the tongue 47into the notch3l of the leg 29 common terminal and the inner edge 67 of the end portion 43 into the notch-30 of the other leg of the common terminal, the notchesserving as abutment meansfor'tensi onin'g the switch blade. Thereafter, the button-equipped cover'23 can'be positioned over the base and secured thereto. f I e The non-actuated position of the switch issh'own in FIG. 1. The tongue 47, which act as the compression member of the snap actionswit'ch. urges the contact 55 carried by the switch blade upwardly into firm electrical engagement with the contact portion 39'of'the normally closed terminal 36. The operating button 56, which engages the central portion of each of the depressed portions 48 of the switch blade is maintained by the switch blade in the position illustrated in which the shoulders 61 and 62 thereof engage the top wall of the cover. The switch blade is advantageously sized relative to the common terminal 26 so that the tongue 47 is substantially straight when the switch is in the nonactuated position illustrated in FIG. 1, but the tongue may be bowed slightly downwardly toensure that the tongue will bow in the right direction when the switch is actuated.

The length of the Switchblade and the length of the tongue 47 is sized relative to the distance between the notches in the two legs of the common terminal so that the tongue 47 exerts a tension force on the legs of the switch blade which tends to straighten or flatten the bent portions 48 and 49 of the legs. Referring to FIGS. I1 and 11A. a tension force T is exerted on the straight portions of the legs by the tongue 47, and this causes a tension force T- to be exerted on the fibers within the upper half of the bent portion 48 and a compression force C. to be exerted on the'flbers within the lower half of the depressed portion. Similar tension and com pression forces are exerted in the raised portions 49, but these need not be disucssed.

The switch is actuated by depressing the operating button 56. The button acts upon the central portion of the depressed portion 48 of each of the legs and moves the spring legs downwardly. As the switch blade moves from the non-actuated position to FIG. I, the spring legs are tensioned andextend somewhat. and a compression force is exerted on the tongue 47. When the switch blade reaches the over-center position, the resil-' ient legs snap the'contact 55 into engagement with the contact portion 35 of the normally opened terminal 33 as shown in FIG. 2. In this position the compression member of tongue 47 is bowed and provides a restoring force to return the switch blade to the FIG. 1 position when the force on the operating button is released.

Referring to FIGS. 12 and I2a, the loading force exerted on the switch blade by the actuating button when then button is depressed is represented by the arrow L, and this load creates a compression force C on the fibers within the upper portion of the depressed portion 48 of each leg and a tension force T on the fibers within the lower portion of the depressed portion. In

conventional switch blades the tension force T created by the operating button causes fatigue failure after a certain number of cycles of'depressing the operating button. However. because the switch blade is prestressed in the area upon which the operating button acts as shown in FIG. 11. the net stresses within the switch blade below the button are very lower during ac- 6- tuation. The prestressed tension force T subtracts from the compression force C created. during actua tion, and 'the, pre'stressed compression; force C 1 sub-I stli lcts from the tension for cev T created during actuation. Although otherswitches have switch blades which are providedjwith curved portions I do not know of any other switch, blade,in, .which the operating button en-.

gages the curvedpo'rtion inamanner to reduce the tension forces created during actuation which contribute to fatigue failure. 7 j I I f A Although the'particular switch bladeQillustratd is provided witha pair of curved portions, one portion 48 extending below the plane of the straight end portions of the blade and the other portion 49 extending above the plane of the straight end portions, lhave had good results with a switch blade having a single curved portion of each leg corresponding to the depressed portion 48. However, I have found that the raised portion 49 is advantageous in maintaining the line of tension in the blade generally in the plane .of the straight portions of the blade and in providing desirable clearance around other structure within the casing such as the leg 29 of the common terminal 27. The spacing between the legs is'sufficient. however, to clear the leg 29 even without the raised portion 49 in the legs. I

The double bends in the legs of the switch blade also increase the overtravel of the switch, i.e.. the distance which the operating-button can travel after the contact is snapped into engagement with the normally opened terminal. The flexibility of the legs provided by the bends permits the button to be depressed a greater distance than would be thecase if the spring legs were straighL'Also, the longer path around the bends of the legs provides more material in the length of the blade so that flexure is distributed to a greater extent.

The capability of substantial overtravel is particularly important when the switch blade 42 is used in a customers assembly in .which thev spacing of the parts or the tolerances thereof might be different. The flexibility of the blade providesgreater reliability. more certainty of actuation, and elimanates other adjustments when multiple installations are made. The switch blade can also be made quite sensitive when that is desirable.

and movement differentials as low as 0.0005 inch are attainable.

In one specific embodiment of the switch. the switch blade was made from .berylium copper having a thick- '7 ness of 0.003. inch. The overall length of the blade was 0.453 inch, and the width of the blade between the outer edges of the spaced-apart legs was 0.l05 inch. The width ofeach of the legs was 0.025 inch, and the l spacing between the legs was 0.055 inch. The length of v the flat central portion 50 of each depressed portion 43. The right end of the flat portion 50, was 0.056 inch was 0.030 inch, and the left end of this flat portion was 0.080 inch from'the inner edge 67 of the end portion from' the center of the raised portionf'49. The curved portions 48 and 49 extended equidistantly vertical distance between the bottom of thedepressed portion 48 above and below the end portions 43"a-nd '44, and the vertical distance between the bottom of ,thedepressed "portion andv the top of the raisedportion 49w'as 0.075 inch; The;st"ress-relieving openings 52 were 0.025 inch in diameter. or about eight times the thickness of the end por'tion-44, and the reinforcing flanges 53 were 0.l30 irich'longand-0.030 inch in width. The diameter of the openings 52 can be varied depending upon the thickness of the switch blade. The diameters of the openings in prior art switch blades were generally limited to about three or four'times the thickness of the blade, but the reinforcing flanges of my blade permit the diameter of the openings to be iniirea'sedsubstantially relative to the thickness of the blade. The flanges become particularly useful when the di ameter is increased to move than five times the thickness of the blade, and the ratio of diameter to thickness can be increased substantially more than eight depending upon the dimensions of the end portion 44 and'the flanges.

Although in the prefer red embodiment, the tension members are provided by a pair ofspaced-apart outer legs, and the compression member is provided by a central tongue, the switch blade could be formed so that the tension member was located between a pair of compression members. In such a case the tension member would still have a prestressed depressed portion below the operating button in which the net stresses during actuation would be very low.

While in the foregoing specification, detailed descriptions of specific embodiments of the invention were set forth for the'purpose of illustration, it is to be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention. I

I claim:

I. An electrical switch comprising a casing, an elongated switch blade having a pair of ends and a contact portion mounted within the casing so that the contact portion thereof is movable between a first position and a second position, the switch blade having a depressed portion between the ends thereof, means biasing the contact portion of the switch blade toward the first position, the biasing means providing a tensile force on the switch blade tending to straighten the depressed portion. and actuating means movably mounted in the casing. the actuating means being received by the depressed portion of the switch blade and being engageable therewith, the actuating means being movable from a first to a second position in the direction in which the depressed portion of the switch blade is depressed. movement of the actuating means from its first position to its second position causing movement of the contact portion of the switch blade from its first position to its second position.

2. The switch of claim 1 in which the biasing means is provided by a tongue portion provided integrally with the switch blade. t

3. The switch of claim 1 in which the switch blade includes a pair of end portions and a pair of spaced-apart leg portions extending between the end portions. said depressed portion being provided in each of the leg portions.

4. The switch of claim 3 in which'the casing means is provided by a tongue portion provided integrally with a line extending between the ends of the switch blade.

7; The switch of claim 1 in which the switch blade iiicludes a pair of end portions and a pair of spaced-apart leg portions extending between the end portions, said depressed portion being provided ineach of the leg pdrtions, the biasing means being provided by a tongue portion provided integrally withthe switch blade and extending from one of the end portions between the leg portions, the tongue portion having a pair of lateral edges, the switch blade having an opening adjacent .the juncture between each lateral edge of the tongue portion and said one end portion,said one end portion having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.

8. The switch of claim 1 in which the switch blade includes a pair of substantailly flat end portions and a pair of spaced-apart leg portions extending between the end portions, the contact portion being provided by one of the end portions, each of the leg portions having a general S-shape provided by a first curved portion extending downwardly from one of the end portions and a second curved portion extending upwardly from the other end portion, the first curved portion ofeach of the leg portions providing the depressed portion'of the switch blade.

9. The switch of claim 8 in which the biasing means is provided by a tongue portion provided integrally with the switch blade and extending from one ofthe end portions between the leg portions.

l0. A snap action electrical switch comprising a casing, a common terminal, a normally closedterminal, and a normally open terminal mounted in the casing, a switch blade movably mounted within the casing and engaging the common terminal, the switch blade having a pair of substantially straight end portions, a pair of spaced-apart leg portions extending between the end portions, each leg portion having a depressed portion extending below the planes of the end portions, and a tongue portion extending from one of the end portions between the leg portions, first abutment means within the casing engaging the tongue portion and second abutment means within the casing engaging one of the end portions whereby the depressed portions are tensioned and the other end portion is biased into engagement with the normally closed terminal, and an actuator movably mounted within the casing above the depressed portions of the legs of the switch blade, the actuator being movable in the direction in which the depressed portions extend below the end portions to engage the depressed portions and to move said other end portion out of engagement with normally closed terminal and into engagement with the normally open terminal.

l l. The switch of claim 10 in which atleast one of the abutment means is provided by the common terminal.

12.,The switch of claim 10 in which the common terminal is generally U-shaped and includes a pair of leg portions, one of .the leg portions of the common terminal providing said first abutment means and the other leg portion of the common terminal providing said second'abutment means.

13. The switch of claim 10 in which each ofthe leg portions of the switchbladeincludes a raised portion 7 adjacent the depressed:;-por.tion,threof. each raised portion extending above the planes of theend portions substantially the same distance as the depressed portions extend below the planes of theend portions.

14. The switch of claim 10 in which the actuator includes a pair of spaced-apart engaging portions and a centering portion extending downwardly between the engaging portions, each of the engaging portions engaging the depressed portion of one of the legs of the switch blade and the centering portion extending downwardly between the legs.

15. The switch of claim 10 in which each depressed portion includes a substantially straight central portion which extends generally parallel to the end portions.

16. The switch of claim 10 in which the tongue portion is substantially straight when said other end engages the normally closed terminal.

17. The switch of claim 10 in which the tongue portion includes a pair of lateral edges, the switch blade having an opening adjacent the juncture between each lateral edge of the tongue portion and said one end portion. said one end having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.

18. The switch of claim 17 in which each opening adjacent the juncture between each lateral edge of the tongue portion has a diameter of at least five time the thickness of the switch blade.

19. An electrically conductive switch blade for an electrical switch having switch blade actuating means, the switch blade having a pair of end portions, a tension member extending between the end portions, and a compression member extending from one of the end portions, the tension member being formed of flexible and resilient material and having a depressed portion extending below the end portions of the switch blade, the switch blade being adapted to be mounted within the switch so that the depressed portion is prestressed by the compresssion member and is positioned below the actuating means whereby engagement of the depressed portion by the actuating means to move the switch blade reduced the net tension forces within the depressed portion.

20. The structure of claim 19 in which the switch blade is provided with an opening in said one end portion adjacent the juncture between the tension member and the compression member, the opening having a diameter of at least five times the thickness of the end portion.

21. The structure of claim 20 including a reinforcing flange extending from said one end portion generally perpendicularly thereto.

22. The structure of claim 19 in which the tension member comprises of spaced-apart leg portions extending between the end portions, said depressed portion being provided in each of the leg portions. the compression member being provided by a tongue portion provided intergrally with the switch blade and extending from said one end portion between the leg portions. the tongue portion having a pair of leteral edges, the switch blade having an opening in said one end portion adjacent the juncture between each lateral edge of the tongue portion and the adjacent leg portion, said one end portion having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.

23. The structure of claim 22 in which said openings have a diameter of at least five times the thickness of the end portion. 

1. An electrical switch comprising a casing, an elongated switch blade having a pair of ends and a contact portion mounted within the casing so that the contact portion thereof is movable between a first position and a second position, the switch blade having a depressed portion between the ends thereof, means biasing the contact portion of the switch blade toward the first position, the biasing means providing a tensile force on the switch blade tending to straighten the depressed portion, and actuating means movably mounted in the casing, the actuating means being received by the depressed portion of the switch blade and being engageable therewith, the actuating means being movable from a first to a second position in the direction in which the depressed portion of the switch blade is depressed, movement of the actuating means from its first position to its second position causing movement of the contact portion of the switch blade from its first position to its second position.
 2. The switch of claim 1 in which the biasing means is provided by a tongue portion provided integrally with the switch blade.
 3. The switch of claim 1 in which the switch blade includes a pair of end portions and a pair of spaced-apart leg portions extending between the end portions, said depressed portion being provided in each of the leg portions.
 4. The switch of claim 3 in which the casing means is provided by a tongue portion provided integrally with the switch blade and extending from one of the end portions between the leg portions.
 5. The switch of claim 4 in which the tongue portion is substantially flat when the contact portion is in its first position, movement of the contact portion to second position causing bending of the tongue portion.
 6. The switch of claim 1 in which the depressed portion extends below a line extending between the ends of the switch blade, the switch blade having a raised portion between the ends thereof which extends above a line extending between the ends of the switch blade.
 7. The switch of claim 1 in which the switch blade includes a pair of end portions and a pair of spaced-apart leg portions extending between the end portions, said depressed portion being provided in each of the leg portions, the biasing means being provided by a tongue portion provided integrally with the switch blade and extending from one of the end portions between the leg portions, the tongue portion having a pair of lateral edges, the switch blade having an opening adjacent the juncture between each lateral edge of the tongue portion and said one end portion, said one end portion having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.
 8. The switch of claim 1 in which the switch blade includes a pair of substantailly flat end portions and a pair of spaced-apart leg portions extending between the end portions, the contact portion being provided by one of the end portions, each of the leg portions having a general S-shape provided by a first curved portion extending downwardly from one of the end portions and a second curved portion extending upwardly from the other end portion, the first curved portion of each of the leg portions providing the depressed portion of the switch blade.
 9. The switch of claim 8 in which the biasing means is provided by a tongue portion provided integrally with the switch blade and extending from one of the end portions between the leg portions.
 10. A snap action electrical switch comprising a casing, a common terminal, a normally closed terminal, and a normally open terminal mounted in the casing, a switch blade movably mounted within the casing and engaging the common terminal, the switch blade having a pair of substantially straight end portions, a pair of spaced-apart leg portions extending between the end portions, each leg portion having a depressed portion extending below the planes of the end portions, and a tongue portion extending from one of the end portions between the leg portions, first abutment means within the casing engaging the tongue portion and second abutment means within the casing engaging one of the end portions whereby the depressed portions are tensioned and the other end portion is biased into engagement with the normally closed terminal, and an actuator movably mounted within the casing above the depressed portions of the legs of the switch blade, the actuator being movable in the direction in which the depressed portions extend below the end portions to engage the depressed portions and to move said other end portion out of engagement with normally closed terminal and into engagement with the normally open teRminal.
 11. The switch of claim 10 in which at least one of the abutment means is provided by the common terminal.
 12. The switch of claim 10 in which the common terminal is generally U-shaped and includes a pair of leg portions, one of the leg portions of the common terminal providing said first abutment means and the other leg portion of the common terminal providing said second abutment means.
 13. The switch of claim 10 in which each of the leg portions of the switch blade includes a raised portion adjacent the depressed portion thereof, each raised portion extending above the planes of the end portions substantially the same distance as the depressed portions extend below the planes of the end portions.
 14. The switch of claim 10 in which the actuator includes a pair of spaced-apart engaging portions and a centering portion extending downwardly between the engaging portions, each of the engaging portions engaging the depressed portion of one of the legs of the switch blade and the centering portion extending downwardly between the legs.
 15. The switch of claim 10 in which each depressed portion includes a substantially straight central portion which extends generally parallel to the end portions.
 16. The switch of claim 10 in which the tongue portion is substantially straight when said other end engages the normally closed terminal.
 17. The switch of claim 10 in which the tongue portion includes a pair of lateral edges, the switch blade having an opening adjacent the juncture between each lateral edge of the tongue portion and said one end portion, said one end having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.
 18. The switch of claim 17 in which each opening adjacent the juncture between each lateral edge of the tongue portion has a diameter of at least five time the thickness of the switch blade.
 19. An electrically conductive switch blade for an electrical switch having switch blade actuating means, the switch blade having a pair of end portions, a tension member extending between the end portions, and a compression member extending from one of the end portions, the tension member being formed of flexible and resilient material and having a depressed portion extending below the end portions of the switch blade, the switch blade being adapted to be mounted within the switch so that the depressed portion is prestressed by the compresssion member and is positioned below the actuating means whereby engagement of the depressed portion by the actuating means to move the switch blade reduced the net tension forces within the depressed portion.
 20. The structure of claim 19 in which the switch blade is provided with an opening in said one end portion adjacent the juncture between the tension member and the compression member, the opening having a diameter of at least five times the thickness of the end portion.
 21. The structure of claim 20 including a reinforcing flange extending from said one end portion generally perpendicularly thereto.
 22. The structure of claim 19 in which the tension member comprises of spaced-apart leg portions extending between the end portions, said depressed portion being provided in each of the leg portions, the compression member being provided by a tongue portion provided intergrally with the switch blade and extending from said one end portion between the leg portions, the tongue portion having a pair of leteral edges, the switch blade having an opening in said one end portion adjacent the juncture between each lateral edge of the tongue portion and the adjacent leg portion, said one end portion having a pair of lateral flanges extending generally perpendicularly to the plane of said one end portion.
 23. The structure of claim 22 in which said openings have a diameter of at least five times the thickness of the end portion. 